Spacerless artificial disc replacements

ABSTRACT

Spacerless artificial disc replacements (ADR) are disclosed. One preferred embodiment includes two saddle-shaped components to facilitate more normal spinal flexion, extension, and lateral bending while limit axial rotation, thereby protecting the facet joints and the annulus fibrosus (AF). Either or both of the superior and inferior components are made of a hard material such as chrome cobalt, titanium, or a ceramic including alumina, zirconia, or calcium phosphate. The articulating surfaces of the ADR are also preferably highly polished to reduce friction between the components. Metals, alloys or other materials with shape-memory characteristics may also prove beneficial.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.13/597,898 (“the '898 Application”), filed Aug. 29, 2012 and now U.S.Pat. No. 8,679,182, which is a continuation of U.S. application Ser. No.12/789,925 (“the '925 Application”), filed May 28, 2010 and now U.S.Pat. No. 8,277,507, which is a continuation of U.S. application Ser. No.11/194,786 (“the '786 Application”), filed Aug. 1, 2005 and nowabandoned, which is a continuation of U.S. application Ser. No.10/413,028 (“the '028 Application”), filed Apr. 14, 2003 and nowabandoned, each of said applications also claiming the benefit of thefiling date of U.S. Provisional Patent Application No. 60/372,520, filedApr. 12, 2002, the disclosures of all said applications being herebyincorporated herein by reference. The present application and the '898,'925, '786, and '028 applications also claim the benefit of the filingdate of U.S. Provisional Patent Application No. 60/449,642, filed Feb.24, 2003.

FIELD OF THE INVENTION

This invention relates generally to artificial disc replacements (ADRs)and, more particularly, to devices that operate without softer spacermaterials such as polyethylene.

BACKGROUND OF THE INVENTION

Polyethylene spacers are common in some artificial joint situations,including total knee replacements (TKRs). Polyethylene spacers are alsoused between metal plates in many artificial disc replacement (ADR)designs.

Complications arising from poly debris are well documented, however,including fracture of the spacer once it becomes too thin, absorptionsand migration of poly particles throughout the body, and loosening ofthe bone metal junction as a reaction of the poly debris.

Metal-on-metal and ceramic-on-metal surfaces have much lower wearcharacteristics. In fact, metal-on-metal surfaces demonstrate 400 timesless wear than polyethylene on metal surfaces.

While there have been attempts to limit the use of the poly in ADRdesigns, all existing approaches constitute call-and-socketconfigurations which do not inherently limit axial rotation. Instead,axial rotation is limited through the use of multiple ball-and-socketjoints or an elongated ball-and-socket joint, which complicates thedesign.

SUMMARY OF THE INVENTION

The present invention replaces polyethylene artificial disc replacement(ADR) spacers with harder, more wear resistant materials. In thepreferred embodiments, an ADR according to the invention includesopposing saddle-shaped components to facilitate more normal spinalflexion, extension, and lateral bending. Preferably, the ADR allows atleast 10 degrees of movement on the flexion to extension direction andat least 5 degrees of movement in the lateral bending direction. Thesaddle-shaped articulating surfaces also limit axial rotation, therebyprotecting the facet joints and the annulus fibrosis (AF).

According to the invention, either or both the superior and inferiorcomponents are made of a hard material such as chrome cobalt, titanium,or a ceramic including alumina, zirconia, or calcium phosphate. Thearticulating surfaces of the ADR are also preferably highly polished toreduce friction between the components. Metals, alloys or othermaterials with shape-memory characteristics may also prove beneficial.

The vertebral surfaces of the components may be treated to promote boneingrowth. For example, the vertebral surfaces of the components may haveplasma spray or beads. Alternatively, one or both components may becemented to the vertebrae. The vertebra-facing surfaces may also includeprojections such as keels that fit into the vertebrae. In embodimentsadapted for cementation, one of the components could be made ofpolyethylene or other softer material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an anterior view of an ADR according to the invention;

FIG. 1B is a lateral view of the ADR of FIG. 1;

FIG. 1C is an oblique view of the ADR of FIG. 1;

FIG. 2A is a view of the anterior aspect of an alternative embodiment ofthe ADR;

FIG. 2B is a view of the lateral aspect of an alternative embodiment ofthe ADR shown in FIG. 2B;

FIG. 3A is a view of the anterior aspect of an alternative, lessconstrained, embodiment of the saddle-shaped ADR shown in a fully flexedposition;

FIG. 3B is a view of the lateral aspect of the embodiment of the ADRshown in FIG. 3A;

FIG. 4A is a view of the lateral aspect of another embodiment of asaddle-shaped ADR;

FIG. 4B is a view of the anterior aspect of the embodiment of the ADRshown in FIG. 4A in a fully flexed position;

FIG. 4C is a view of the anterior aspect of an alternative embodiment;

FIG. 4D is a view of the anterior aspect of the ADR shown in FIG. 4A;and

FIG. 4E is a view of the anterior aspect of the ADR shown in FIG. 4A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A is an anterior view of an ADR according to the invention. FIG.1B is a lateral view of the ADR of FIG. 1. FIG. 1C is an oblique view ofthe ADR of FIG. 1.

FIG. 2A is a view of the anterior aspect of an alternative embodiment ofthe ADR, wherein the articulating surfaces of both components have aflat area centrally from the front to the back of the ADR. FIG. 2B is aview of the lateral aspect of an alternative embodiment of the ADR drawnin FIG. 2B. The flat area of the articulating surfaces courses centrallyfrom side of the DR to the other side. The flat area allows onecomponent to translate slightly on the other component. Alternatively, acurved area with a large radius could replace the flat area.

FIG. 3A is a view of the anterior aspect of an alternative, lessconstrained, embodiment of the saddle-shaped ADR drawn in a fully flexedposition. The less constrained embodiment facilitates spinal flexion,extension, and lateral bending. FIG. 3B is a view of the lateral aspectof the embodiment of the ADR drawn in FIG. 3A.

FIG. 4A is a view of the lateral aspect of another embodiment of asaddle-shaped ADR. The center of rotation for flexion and extension isnot necessarily located in the center of the ADR. For example, thecenter of rotation is preferably located in the posterior half of theADR. FIG. 4B is a view of the anterior aspect of the embodiment of theADR drawn in FIG. 4A, drawn in a fully flexed position.

FIG. 4C is a view of the anterior aspect of an alternative embodiment,showing how the radius of curvature of the articulation for lateralbending may be different than the radius of curvature for articulationfor flexion and extension. For example, the radius of curvature for thearticulation for flexion and extension, as seen in FIG. 4A, may besmaller than the radius of curvature for the articulation for lateralbending, as seen in FIG. 4C. Articulating surfaces with smaller radii,facilitate movement. Thus, the embodiment of the ADR drawn in FIG. 4Aflexes and extends more easily than the embodiment of the ADR drawn inFIG. 3A. The ADR is drawn in a fully flexed position.

FIG. 4D is a view of the anterior aspect of the ADR drawn in FIG. 4A.The ADR is drawn in a neutral position. The area of the drawing withdiagonal lines represents the articulating surface of the lower ADRcomponent. FIG. 4E is a view of the anterior aspect of the ADR drawn inFIG. 4A, also drawn in a fully extend position.

The invention claimed is:
 1. A method of implanting an artificial discreplacement comprising: providing an artificial disc replacementcomprising: a first component having a first articulating surface and afirst vertebral contact surface for engaging a first vertebral body, thefirst articulating surface including first and second lateral edges anda toroidal region extending between the first lateral edge and thesecond lateral edge; and a second component having a second articulatingsurface opposed to the first articulating surface and a second vertebralcontact surface for engaging a second vertebral body, the secondarticulating surface including third and fourth lateral edges and atoroidal region extending between the third lateral edge and the fourthlateral edge, wherein the toroidal regions of the first and secondarticulating surfaces of the first and second components arenon-congruent; engaging the first and second vertebral contact surfacesof the first and second components with first and second adjacentvertebral bodies of a spinal column; and articulating the firstcomponent relative to the second component so that the non-congruenttoroidal regions of the first and second articulating surfaces engagewith one another to allow for movement of the first vertebral bodyrelative to the second, adjacent vertebral body.
 2. A method ofimplanting an artificial disc replacement according to claim 1, furthercomprising limiting axial rotation of the first component relative tothe second component to a predefined range.
 3. A method of implanting anartificial disc replacement according to claim 1, wherein the firstarticulating surface is defined by a concave arc having a radius ofcurvature A about a first axis, and a convex arc having a radius ofcurvature B about a second axis perpendicular to the first axis, and thesecond articulating surface is defined by a convex arc having a radiusof curvature C about a third axis, and a concave arc having a radius ofcurvature D about a fourth axis perpendicular to the third axis, theradius of curvature A, D of at least one of the concave arcs beingdifferent than the radius of curvature B, C of at least one of theconvex arcs.
 4. A method of implanting an artificial disc replacementaccording to claim 3, wherein the first and second articulating surfacesare saddle shaped.
 5. A method of implanting an artificial discreplacement according to claim 3, wherein the radius of curvature A, Dof at least one of the concave arcs is greater than the radius ofcurvature B, C of at least one of the convex arcs.
 6. A method ofimplanting an artificial disc replacement according to claim 1, whereinthe toroidal regions of the first and second articulating surfaces,respectively, are defined by continuous curves.
 7. A method ofimplanting an artificial disc replacement according to claim 1, furthercomprising engaging projections extending from the first and secondcomponents with the first and second vertebral bodies, respectively. 8.A method of implanting an artificial disc replacement according to claim7, wherein the projections are selected from the group consisting offlanges and keels.
 9. A method of implanting an artificial discreplacement according to claim 1, wherein the first articulating surfaceincludes a single substantially continuous concave surface and a singlesubstantially continuous convex surface, and the second articulatingsurface includes a single substantially continuous concave surface and asingle substantially continuous convex surface.
 10. A method ofimplanting an artificial disc replacement according to claim 1, whereinthe first and second components are configured to facilitate flexion,extension, and lateral bending of the first and second vertebral bodieswhile limiting axial rotation.
 11. A method of implanting an artificialdisc replacement comprising: providing an artificial disc replacementcomprising: a first component having a first articulating surface and afirst vertebral contact surface for contacting a first vertebral body,the first articulating surface including a toroidal region with a firstcontinuous convex arc and a first continuous concave arc, wherein thefirst articulating surface is defined by first and second lateral edges,the first continuous concave arc spanning between the first and thesecond lateral edge; a second component having a second articulatingsurface engaged with the first articulating surface and a secondvertebral contact surface for contacting a second vertebral body, thesecond articulating surface including a toroidal region with a secondcontinuous convex arc and a second continuous concave arc, wherein thesecond articulating surface is defined by third and fourth lateraledges, the second continuous convex arc spanning between the third andthe fourth lateral edge, and wherein the toroidal regions of the firstand second articulating surfaces of the first and second components arenon-congruent; engaging the first and second vertebral contact surfacesof the first and second components with first and second adjacentvertebral bodies of a spinal canal column; and articulating the firstcomponent relative to the second component so that the non-congruenttoroidal regions of the first and second articulating surfaces engagewith one another to allow for movement of the first vertebral bodyrelative to the second, adjacent vertebral body.
 12. A method ofimplanting an artificial disc replacement according to claim 11, whereinthe first continuous concave and convex arcs each has a respectiveradius of curvature, and the second continuous concave and convex arcseach has a respective radius of curvature, the radius of curvature of atleast one of the concave arcs being different than the radius ofcurvature of at least one of the convex arcs.
 13. A method of implantingan artificial disc replacement according to claim 11, further comprisinglimiting axial rotation of the first component relative to the secondcomponent to a predefined range.
 14. A method of implanting anartificial disc replacement according to claim 13, wherein the firstconcave arc has a radius of curvature A about a first axis and the firstconvex arc has a radius of curvature B about a second axis perpendicularto the first axis, and wherein the second convex arc has a radius ofcurvature C about a third axis and the second concave arc has a radiusof curvature D about a fourth axis perpendicular to the third axis. 15.A method of implanting an artificial disc replacement according to claim14, wherein the radius of curvature A, D of at least one of the concavearcs is greater than the radius of curvature B, C of at least one of theconvex arcs.
 16. A method of implanting an artificial disc replacementaccording to claim 11, further comprising engaging projections extendingfrom the first and second components with the first and second vertebralbodies, respectively.
 17. A method of implanting an artificial discreplacement according to claim 16, wherein the projections are selectedfrom the group consisting of flanges and keels.
 18. A method ofimplanting an artificial disc replacement according to claim 11, whereinthe first and second components are configured to facilitate flexion,extension, and lateral bending of the first and second vertebral bodieswhile limiting axial rotation.
 19. A method of implanting an artificialdisc replacement according to claim 11, wherein the first and secondarticulating surfaces are saddle shaped.